#define _CRT_SECURE_NO_WARNINGS 1
int main(void)
{
    float r1 = 0.0f, r2 = 0.0f;
    float r3 = 0.0f;
    scanf("%f%f", &r1, &r2);
    r3 = (r1 * r2) / (r1 + r2);
    printf("%.1f", r3);
    return 0;
}
